Mathematical modeling of the heart using magnetic resonance imaging

A hybrid three-dimensional solid mathematical model of cardiac ventricular geometry developed using magnetic resonance (MR) images of an in vivo canine heart is discussed. The modeling techniques were validated using MR images of an ex vivo heart and direct measurements of cardiac geometry and mass properties. A spin-echo MR sequence with in-plane resolution of 1.0 mm was used to image the canine heart in eleven short-axis planes at contiguous 5-mm intervals. Contour points on the epicardial, left ventricle (LV), and right ventricle (RV) boundaries were selected manually at each slice level. A boundary representation geometric model was constructed by fitting third-order nonuniform rational B-spline surfaces through each set of surface points. Compared to the anatomic specimen (AS), volume errors of the ex vivo model were 0.3, 1.5, and 5.8% for the LV cavity, RV cavity, and total enclosed volumes, respectively. Comparison of cross-sectional areas of the AS and the model at ten levels demonstrated mean model errors of 4.1, 2.5, and 2.9% for the LV, RV, and epicardial boundaries, respectively     

Fabrication and characterization of APT specimens from high dose heavy ion irradiated materials

The next generations of advanced energy systems will require materials that can withstand high doses of irradiation at elevated temperatures. Therefore, a methodology has been developed for the fabrication of high-dose ion-irradiated atom probe tomography specimens at a specific dose with the use of a focused ion beam milling system. The method also enables the precise ion dose of the atom probe tomography specimen to be estimated from the local concentration of the implanted ions. The method has been successfully applied to the characterization of the distribution of nanoclusters in a radiation-tolerant 14YWT nanostructured ferritic steel under ion irradiation to doses up to 400 displacements per atom.     

Temperature distributions in laser-heated semi-infinite and finite-thickness media with convective surface losses

The temperature distributions produced within semi-infinite and finite-thickness media heated by a moving laser beam with a Gaussian power-density profile are examined by use of a time-domain method. Convective losses, described by Newton's law of cooling, from the medium surfaces are included. Various medium absorption models are considered. The solutions are given as single integrals with respect to time of simple functions. The resulting expressions have been used to examine the role of surface losses in information storage and medical applications. The role of convective losses in optical recording systems is found to be insignificant. However, for medical applications, combined convective and evaporative surface losses represent an important surface-heat-loss mechanism.     

Spectroscopic ellipsometry of slightly inhomogeneous nonabsorbing thin films with arbitrary refractive-index profiles: theoretical study

We develop a new approximation for the amplitude reflection coefficients of a slightly inhomogeneous thin film. This approximation incorporates exactly the interference effects at the substrate and the ambient interfaces. Interference effects inside the inhomogeneous film are incorporated in the Born approximation. We also develop a new approach to the reconstruction of the refractive-index profile from ellipsometric spectra. It is based on a physically sound parameterization of the refractive-index profile. The new approach is tested on the model reconstruction problem.     

Optoelectronic Recoded and Nonrecoded Trinary Signed-Digit Adder that uses Optical Correlation

A symbolic-substitution-based optical numeric processor that uses recoded and nonrecoded trinary signed-digit (TSD) number representations is proposed. Also, we propose new joint spatial encodings for the TSD numbers that reduce the symbolic-substitution computation rules involved in the processor. Optoelectronic implementation of the proposed recoded adder is feasible. Also, the nonrecoded TSD addition can be performed optically in two steps. Both the proposed recoded and nonrecoded adders are more compact than a recently reported modified signed-digit counterpart and use fewer correlators and spatial light modulators.     

Application of the needle optimization technique to the design of optical coatings

The authors' experience with the application of the needle optimization technique to the design of optical coating is summarized. A physical interpretation of the technique is provided, and its main features are identified. Guidelines on the application of the needle optimization technique to various types of design problems are given.     

Robust multiscale stereo matching from fundus images with radiometric differences

A robust multiscale stereo matching algorithm is proposed to find reliable correspondences between low contrast and weakly textured retinal image pairs with radiometric differences. Existing algorithms designed to deal with piecewise planar surfaces with distinct features and Lambertian reflectance do not apply in applications such as 3D reconstruction of medical images including stereo retinal images. In this paper, robust pixel feature vectors are formulated to extract discriminative features in the presence of noise in scale space, through which the response of low-frequency mechanisms alter and interact with the response of high-frequency mechanisms. The deep structures of the scene are represented with the evolution of disparity estimates in scale space, which distributes the matching ambiguity along the scale dimension to obtain globally coherent reconstructions. The performance is verified both qualitatively by face validity and quantitatively on our collection of stereo fundus image sets with ground truth, which have been made publicly available as an extension of standard test images for performance evaluation.     

Mild body cooling impairs attention via distraction from skin cooling

Many contemporary workers are routinely exposed to mild cold stress, which may compromise mental function and lead to accidents. A study investigated the effect of mild body cooling of 1.0 degree C rectal temperature (Tre) on vigilance (i.e. sustained attention) and the orienting of spatial attention (i.e. spatially selective processing of visual information). Vigilance and spatial attention tests were administered to 14 healthy males and six females at four stages (pre-immersion, deltaTre = 0, -0.5 and - 1.0 degree C ) of a gradual, head-out immersion cooling session (18-25 deltaC water), and in four time-matched stages of a contrast session, in which participants sat in an empty tub and no cooling took place. In the spatial attention test, target discrimination times were similar for all stages of the contrast session, but increased significantly in the cooling phase upon immersion (deltaTre = 0 degrees C), with no further increases at deltaTre = -0.5 and - 1.0 degree C. Despite global response slowing, cooling did not affect the normal pattern of spatial orienting. In the vigilance test, the variability of detection time was adversely affected in the cooling but not the contrast trials: variability increased at immersion but did not increase further with additional cooling. These findings suggest that attentional impairments are more closely linked to the distracting effects of cold skin temperature than decreases in body core temperature.